(1) Field of the Invention
The present invention relates to methods used to fabricate semiconductor devices, and more specifically to a method used to form a stacked capacitor structure, with increased surface area, for a dynamic random access memory (DRAM) device.
(2) Description of Prior Art
Micro-miniaturization, or the ability to fabricate semiconductor devices using sub-micron features, have allowed the performance of these semiconductor devices to be unproved while still decreasing the processing cost of a specific sub-micron device. Dimension reduction, realized via the use of sub-micron features, has resulted in decreases in performance degrading parasitic capacitances. In addition the use of sub-micron features have resulted in a greater number of smaller semiconductor chips attainable from a specific size starting substrate, with device densities of the smaller semiconductor chips still equal to or greater than counterpart larger semiconductor chips fabricated using larger dimensions, thus allowing the processing cost for a specific semiconductor chip to be reduced. However in the area of DRAM technology, the decreasing size of the transfer gate transistor limits the horizontal dimension of an overlying DRAM capacitor structure. To continually increase device performance capacitance increases, or increases in the ice area of the capacitor structure, have to be achieved, however without increasing the horizontal dimension of the capacitor structure. The increased surface area for DRAM stacked capacitor structures, are usually achieved via unique geometric configurations such as crown, cylindrical or fin shaped structures in which additional vertical features are formed as part of the stacked capacitor structure. However to achieve these unique configurations rigorous and complex process sequences are needed, adding additional process cost.
This invention will teach a method of forming a stacked capacitor structure offering increased surface area, however without forming the complex vertical and protruding horizontal features comprised in the crown, cylindrical or fin type structure. This invention will feature a xe2x80x9cneckedxe2x80x9d profile for a capacitor structure, comprised with necked regions, or lateral grooves located in, and extending from, the sides of capacitor storage node structure. The necked capacitor profile, obtained via multiple ion implantation procedures into, and conventional dry etching of, a storage node structure, can result in a capacitor structure exhibiting a surface area of about 3 times greater than a surface area achieved with flat surfaces. Prior art, such as Forbes et al, in U.S. Pat. No. 6,025,225, describe a method of roughening the surface of a trench capacitor structure, while Jun in U.S. Pat. No. 5,691,221, describe a method of forming a fin type, stacked capacitor structure. However neither of these prior arts describe a process for forming the novel, capacitor structure, featuring the necked profile, now described in this present invention.
It is an object of this invention to fabricate a DRAM device, on a semiconductor substrate.
It is another object of this invention to form a DRAM stacked capacitor structure, featuring a storage node structure with a necked profile, employed to increase the capacitor surface area.
It is still another object of this invention to form the necked profile, for the DRAM capacitor structure, via multiple ion implantation procedures, performed at various energies, placing groups of implanted ions at specific depths in a polysilicon storage node structure, followed by a dry etch procedure which laterally removes the implanted regions at a greater rate than the non-implanted regions of the storage node structure, resulting in the desired grooves, or the necked profile, for the polysilicon storage node structure of the DRAM capacitor device.
In accordance with the present invention a method of fabricating a DRAM capacitor structure, comprised with a storage node structure featuring a necked profile, used for surface area increases, is described. After formation of an underlying transfer gate transistor, a storage node plug structure is formed in an insulator layer, overlying and contacting a portion of a top surface of the transfer gate transistor source/drain region. An intrinsic polysilicon layer is deposited on the top surface of the insulator layer, overlying and contacting the top surface of the storage node plug structure. A series of ion implantation procedures is performed at multiple implant energies, placing layers of implanted ions in specific regions of the intrinsic polysilicon layer, with intrinsic, or non-implanted regions of polysilicon located between the implanted regions. A dry etch procedure is used to vertically define the polysilicon storage node structure, with the dry etch procedure also laterally, and selectively removing portions of the implanted regions located at the outside surface of the defined storage node structure, resulting in the necked profile storage node structure. After deposition of a capacitor dielectric layer on the necked profile, storage node structure, an upper electrode is formed resulting in a DRAM capacitor structure featuring increased sure area as a result of formation of the storage node structure with the necked profile.